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280 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

Column (8) is 12 m high and 0.35 m in diameter. Here m- nitrotoluene is dis-

tilled off. p- Isomer flows to the lower part of the column. The column is heated

through valve (23) and boiler (7) by means of a coil. The vapours leaving the column

are condensed in (9) and cooled with water passing through (28).

Most of the condensed vapour returns to the column, and the rest flows down

through (21) via a flowmeter and the pump (17) to a storage tank. Samples are taken

through the valves near the pump and the setting point of the product is deter-

mined.

p- Nitrotoluene which falls into the lower part of the second column is trans-

ferred through the pump (16) to a crystallizer. Some of the p- nitrotoluene returns

through (26) to the column if the level in the column is too low. Thermometers

(30) serve to control the process.

TABLE 53

SPECIFICATION FOR O- NITROTOLUENE (AFTER U.S.S.R. DATA, GORST [2])

I grade II grade

Appearance Clear oily liquid of a light

yellow to light brown colour

Boiling range

not less than 90 vol. %

at 760 mm Hg pressure should

distil between 218-223°C 217-223.5ºC

Dinitrotoluene none

Hydrocarbons below 0.1% below 0.1%

p- Nitrotoluene below 1% below 2%

Moisture below 0.1% below 0.1%

TABLE 54

SPECIFICATION FOR P-NITROTOLUENE (AFTER U.S.S.R. DATA, GORST [2])

I grade II grade

Appearance light grey to light yellow crystals

Freezing point, not below 50°C 49°C

Dinitrotoluene none

Hydrocarbons none

Moisture below 1%

Toluene insoluble substances below 0.1%

Distillation in both columns occurs in the upper parts under a reduced pres-

sure of 10 mm Hg. The vacuum pipe is connected with condensers (6) and (9) and

expansion vessels (18) (19) (20) (21) and with the regulatingvalve (24). The vapours

which penetrate into the vacuum pipe, are condensed in condenser (10) and flow

down through (18). All pipes for m- and p- nitrotoluene should be insulated to avoid

solidification of the products.

Preparation of pure isomers. Since the isolation of high purity o- and m- isomers

from a mixture obtained by direct nitration is rather difficult, the very pure sub-

stances have been obtained by indirect methods.